1. Field of the Invention
The present invention relates to an electric double layer capacitor, particularly to a separator sheet used for manufacturing the electric double layer capacitor, and a method for manufacturing the same.
2. Description of the Related Art
The electric capacity of a conventional capacitor is generally determined by the dielectric constant of the dielectric material interposed between two oppositely disposed electrodes.
However, an electrical double layer capacitor has a different feature from conventional capacitors using dielectric material in that positive charge and negative charge are distributed with a considerably short distance around the interface between two different layers of a solid and a liquid.
The layer formed around the interface is referred to as Electric Double Layer, and the capacitor using it is classified as electric double layer capacitor.
For the solid of the electric double layer capacitor, it is preferable to use a material having large specific surface area so that more electric double layers are formed to obtain large capacity. Accordingly, activated carbon or activated fiber whose surface area is more than 1000 m2/g, and diluted sulphuric acid, can be employed for the solid and the liquid, respectively, to result in a considerably higher capacity of F (Farad) level of capacitor than conventional capacitor.
The electric double layer capacitor has intermediate characteristics between an electrolytic capacitor and a secondary battery, and is an energy storage device that has high efficiency, excellent durability, and fast charge/discharge ability. Thus, the electric double layer capacitor may be used in combination with a conventional secondary battery, or be a substitutable energy storage device for it.
In addition, the electric double layer capacitor can input/output energy within a short time, and thus may be used for rectifier circuit, noise attenuation, and pulse generation for power supply unit. Moreover, the capacitor's capacitance is highly increased, compared with other electric chemical condenser, and so the electric double layer capacitor has high output of pulse power capacity and high energy storage capacity. Thus, the electric double layer capacitor may be applicable for a compact electrochemical energy storage device and load leveling of high output of pulse power and peak power.
Further, the electric double layer capacitor has been more important environmentally and economically among other energy storage devices in that it uses environmentally friendly materials, and has long life span and high charge/discharge efficiency. This electric double layer is expected to be used for a main power supply source and an auxiliary power supply source of high output of pulse power for highly value added equipments in various technical fields such as military defense, aerospace, medical equipment, HEV, etc.
FIG. 1A is a cross-sectional view of a conventional electric double layer capacitor, illustrating a schematic structure of the electric double layer capacitor, and FIG. 1B is a schematic view of the basic cell illustrated in FIG. 1A.
Referring to FIG. 1A, an electric double layer capacitor 1 comprises at least one basic cell 10. Here, the multilayer cell 20 manufactured by stacking 5 basic cells 10 in series is illustrated. An electrode plate 21 with its lead terminal is attached to outer surface of the basic cells 10 disposed in the outermost positions, and an outer package 22 is covering the electrode plate 21. The packaging is performed under pressure reduced condition.
The lead terminal attached to the electrode plate 21 is made by doing solder plating on the surface of copper plate, and made up of a flat electrode plate body 24 and a band-shaped lead terminal 25 extended from the electrode plate body 24, wherein the electrode plate body 24 is bonded to the outer surface of the outermost basic cells 10 of the multilayer cell 20.
Referring to FIG. 1B, the basic cell 10 comprises a porous separator 11 in the form of a sheet; a pair of current collector films 12 oppositely disposed relatively to the separator 11; a pair of polarized electrodes 13 disposed between the separator 1 and the current collect films 12; and a frame form of gasket 14 which is laterally contiguous to the separator 11 and the polarized electrodes 13 and interposed between the pair of current collector films 12. The basic cell 10 is sealed with an electrolytic solution therein.
The steps for manufacturing the basic cell 10 are described with reference to FIG. 2 below.
FIG. 2 is a view illustrating some of the steps for manufacturing an electric double layer capacitor.
As shown in FIG. 2(a), a current collector film 12 is prepared, and cut to be a certain size as shown in FIG. 2(b). The current collector film 12 is a conductive film made up of an insulation resin and a conductive material.
Next, as shown in FIG. 2(c), a frame form of gasket 14 is installed on the surface of the current collector film 12. As the gasket 14 is positioned at the edge of the current collector film 12, a portion of the current collector film 12 is exposed inside the gasket 14.
Next, as shown in FIG. 2(d), a polarized electrode 13 is formed on the surface of the exposed current collector film 12, and as shown in FIG. 2(e), a separator 11 is disposed to cover inside of the gasket.
Next, as shown in FIG. 2(f), two intermediate structures formed from FIG. 2(a) to FIG. 2(d) are oppositely disposed with having the separator 11 in between.
Finally, the structure shown in FIG. 2(f) is thermo-compressed for the gaskets 14 to be thermally fusion-bonded to each other, to complete the basic cell shown in FIG. 2(g).
However, in case that basic cell array including a plurality of basic cells is produced from one current collector film, there is a difficult problem that a plurality of separators should be aligned precisely on each corresponding gasket. Therefore, there has been a need to develop a method to dispose the separators easily and precisely on their respective gaskets.